PSI - Issue 57

J. Torggler et al. / Procedia Structural Integrity 57 (2024) 152–160 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

155

4

Longitudinal Y (F y , V)

F y

F y

F y

- + fibre angle

U

U

Lateral X (F x , U)

Sample geometry and coordinate system

Step 0: Longitudinal preload

Step 1: Lateral displacement

Figure 2: Flat sample geometry with coordinate system and testing procedure

To ensure that all tests start in the same condition, the sample is pre-conditioned with a defined cycle based on European Standard EN 13597:2003 E (2008) . After the standardised conditioning, the actual test is started. Figure 2 shows the test procedure. In step 0, a longitudinal preload F y is applied to the specimen to map the internal pressure p i in the air spring bellow. Under constant longitudinal preload F y (deviation < ±2.5%), a displacement-controlled constant lateral displacement amplitude U is applied cyclically to the specimen, shown in step 1. The lateral force F x should stay symmetrical over the whole test (deviation < ±1.5%). The test frequency is limited by a maximum surface temperature of 50 °C, so that there is no notable change of the material properties. Representative for all the tests carried out on different assemblies, one sample is discussed in detail here (number 19 with four layers and a fibre angle of 15 degree). The measured data from both axes X and Y , force and displacement are recorded while fatigue testing. In this case, the set longitudinal preload was F y = 5.8 kN and the lateral displacement amplitude U = 23 mm. Figure 3 left shows the amount of the maximum and minimum lateral force F x per oscillation cycle. At the right the mean value of the longitudinal displacement V is plotted over the load changes. Three different areas can be seen for this parameter, similar to Tian et al. (2001). Up to a number of 100 load-cycles a run-in behaviour, then a relatively linear increase of the travel and towards the end a somewhat stronger increase is noticeable. Based on a comprehensive analysis of the test results and failure mechanisms, a 20 % increase in this parameter is chosen as failure criterion for the fatigue tests in order to define an appropriate and comparable number of load-cycles.

Figure 3: Maximum and minimum shear force F x over number of load cycles (left) and mean value of the longitudinal displacement V over number of load-cycles (right) for one representative specimen